Why we swing our arms as we walk

Biomedical researchers on Wednesday said they could explain why we swing our arms when we walk, a practice that has long piqued scientific curiosity. Arm-swinging turned out to be a plus, rather than a negative, they found. For one thing, it is surprisingly, er, “‘armless” in energy costs, requiring little torque, or rotational twist, from the shoulder muscles.

Biomedical researchers on Wednesday said they could explain why we swing our arms when we walk, a practice that has long piqued scientific curiosity.

A trio of specialists from the United States and the Netherlands built a mechanical model to get an idea of the dynamics of arm-swinging.

They recruited 10 volunteers, who were asked to walk with a normal swing, an opposite-to-normal swing, with their arms folded or held by their sides.

The metabolic cost of this activity was derived from oxygen consumption and carbon dioxide production as the human guinea pigs breathed in and out.

Arm-swinging turned out to be a plus, rather than a negative, they found. For one thing, it is surprisingly, er, “‘armless” in energy costs, requiring little torque, or rotational twist, from the shoulder muscles.

Holding one’s arms as one walks requires 12 per cent more metabolic energy, compared with swinging them. The arms’ pendulum swing also helps dampen the bobbly up-and-down motion of walking, which is itself an energy drain for the muscles of the lower legs.